Scroll down to avoid tapping on nav bar

The test failed on phone target with ROTATION_90 and MODE_GESTURAL
because the button click can accidentally trigger a recent transition.

Adding a bottom padding, and scrolling to the bottom before clicking
the button to prevent this from happening.

Bug: 341209752
Test: atest FlickerTestsActivityEmbedding:OpenTrampolineActivityTest
Flag: EXEMPT test fix
Change-Id: Ifd240902d88532cee714ed624d8e08aaafb58324